Method of and material for treating metal



Patented Sept. 7, 1943 METHOD or AND MATERIAL FOR TREATING METAL Carroll A. Hochwalt. Dayton, Ohio, assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation 01 Delaware No Drawing. Application June Serial No. 339,574

15 Claims.

This invention relates to methods and materials for the cold working of metal, and particularly relates to methods and materials suitable for use in deep drawing operations.

In prior cold working processes, such as machining, drawing, punching, stamping, and the like, it has been customary to lubricate the metal with oil,- grease, degras soaps, or the like. Such substances, however, are highly undesirable because of the difficulty of removing the same prior to subsequent operations such as finishing, coating, or the like. Substances such as oil or grease, for example, cannot be thoroughlyremoved by a simple water rinse, with the result that frequently the surface of the metal appears clean and bright, but actually has retained suificient residual grease to markedly interfere with proper finishing. pounds, hard soaps are formed, particularly when working with copper or brass, and when annealing operations are employed, as in the drawing of the side panels of refrigerator cabinets.

charring occurs with the formation of resinous materials which are extremely difiicult-to remove. Also when employing these substances relatively high working temperatures occur with 'vide a lubricant for the above stated purposes which is capable of lowering the temperatures developed during working and thereby markedly decreasing the number of cracked or galled products. a It is a further object of the invention to provide an eflicient lubricant or bath of the type described which is easy to prepare, relatively inexpensive, and substantially neutral and noncorrosive.

A still further object of the invention is to provide a lubricant having the abov desirable properties and in addition possessing considerable rust-prooflng power.

Still further objects and advantages-of the invention will appear from the following description and appended claims. Before explaining in detail the present invention, however, it is to be understood that the invention is not limited in its application to the details described herein, since the invention is, capable of other embodiments and of being practiced or carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein Likewise, when using degras comis for the purpose of description and not of limitation, and it is not intended to limit the invention claimed herein beyond the requirements of the prior art.

general the invention relates to the use of aqueous solutions or suspensions of certain alkyl phosphate compounds, preferably those lying within a certain viscosity range and having the properties of being readily soluble in water and stable at working temperatures, as lubricants for metal working purposes. These solutions or baths may be of varying strength, but for purposes. of economy they need not contain more than 50% by weight of the alkyl phosphate and in many instances can be satisfactorily employed in,

strengths of as low as 20% by weight. It is preferred to use them in the form of their so dium salts, as these are the cheapest. Of these, sodium ethyl phosphate is the most satisfactory, because of its oiliness and high viscosity, yet other alkyl phosphates, such as the equivalent methyl, propyl and butyl phosphates ma also be used with advantage, and if desired the equivalent potassium salts may be employed. The preferred viscosity range referred to is that comparable to or substantially close to the viscosity.

of sodium ethyl phosphate mixtures, which to all intents and purposes are the most suitable compound of all for the purposes of the present invention. These compounds, particularly those mixtures containing about 40% of the monoethyl and 60% of the diethyi derivative, have viscosities varying from about 2.5 to centipoises at 25 C. when used in-the amounts and concen-- trations described herein. In many'instances. however, it is possible to use phosphate derivatives having viscosities as high as 300 centipoises at 25 C. i

Purely inorganic phosphate salts, such as dipotassium, mono-sodium, and mono-ammonium phosphate, have been employedby John L. Tufts (Patent No. 2,008,939) for the same purpose as in the present invention. These salts, however, must be used in solutions of greater concentration than the alkyl phosphates of the present invention, and even at higher concentrations are not as satisfactory because'of the higher temperature'of the metal pieces coming from the die and the higher percentage of rejects due to tearing and cracking of the metal sheets. Moreover, mono-sodium and mono-ammonium phosphates are slightly acid (pH of about. 4.4 to 4.9 in a. 1% solution) and therefore tend to exert an undesirable corrosive action on the metal.

The various alkyl salts of the type described herein may be prepared by first reacting a phosphorus oxide containing substance with a monohydric aliphatic alcohol, and then neutralizing the reaction product with a basically reacting substance to form the corresponding salt.

. The neutralization reaction to form the corresponding sodium salts may be typified as follows:

The R in each of the above six equations represents an alkyl radical.

The neutralizationshown above can, of course, be efiected with substances other than sodium carbonate or sodium hydroxide. Thus, potassium or ammonium compounds may be used in the same manner for the production of monoor di-alkyl potassium or ammonium phosphates. Amines may also be employed and a particularly desirable product may be obtained by the use of triethanolamine or other hydroxy alkyl amines. For most purposes a final pH of from 6 to 8.5 will be found satisfactory.

For the purpose of this invention, it is, not necessary separately to recover the reaction prod.- ucts in the mixture of alkyl phosphates produced by the action of phosphorus pentoxide'or a strong phosphoric acid with anhydrous aliphatic alcohols. The process of neutralization, however, is made more simple if the trialkyl phosphate content of the mixture belkept at aminim'um. When a mixture of varying proportions of monoand di-alkyl phosphates is neutralized with a basically reacting compound, a mixture of water-soluble, substantially neutral monoand di-alkyl phosphate salts is obtained. These salts are hygroscopic and possess lubricating qualities: in aqueous solutions which render them of outstanding value as lubricants for use in metal working operations.

Typical of some of the compounds which may be employed in accordance with the present invention are the following:

Monosodium diethyl phosphate, Monosodium din-butyl phosphate, Disodium monoethyl phosphate, Monosodium dimethyl phosphate, Disodium monomethyl phosphate,

Monoam'monium diethyl phosphate,

Diammonium monoethyl phosphate, Triethylamine diethyl phosphate, Diethylamine diethyl phosphate, Monoethylamine diethyl phosphate, Di (triethylamine) monoethyl phosphate,

Di (diethylamine) monoethyl phosphate,

phosphate.

Triethanolamine di n-butyl phosphate, Triethanolamine diisobutyl phosphate, Trimethanolamine diethyl phosphate,

Di (trimethanolamine) monoethyl phosphate, Triethanolamine dimethyl phosphate, Monopotassium diethyl phosphate,

Dipotassium monoethyl phosphate,

Potassium sodium monoethyl phosphate, Monopotassium monoethyl hydrogen phosphate, Monosodium monoethyl hydrogen phosphate.

In general, any salt of an alkyl. phosphoric acid which is within the desired viscosity range and whose aqueous solutions have lubricating properties may be employed in carrying out the present invention. Mixtures of any of the above materials mayalso be employed to prepare the solutions or baths of the present invention, and, in fact, it is usually preferable from a cost standpoint to employ mixtures.

A typical lubricant bath according to the present invention contains from 20% to 50% of sodium ethyl phosphate in an aqueous solution, in which the phosphate consists of about of diethyl and about 3.5% of monoethyl sodium To this bath may be added, if desired, small amounts of a wetting agent and/or a corrosion inhibitor. For example from .1 to .5% of a wetting agent and from .1 to 25% of a corrosion inhibitor may be employed. The wetting agent should consist of a hydrophobic and a hydrophilic group. For example, the sodium salts of alkylated benzene sulfonates and mixtures thereof, particularly those derivatives having from 1D to 15 carbon atoms in the alkyl group, are suitable wetting agents for the purpose, while any of the common inhibitors of metal corrosion such as sodium dichro'mate or ammonium molybdate may be used as the corrosion inhibitor. Thus a typical bath for the purposes of the present invention contains the following in aqueous solution: 7

Per cent by weight The .resulting compound is very effective for use in deep drawing operations, and it will be found that a noticeably small percentage of rejects due to excoriations'or galling will occur. This is undoubtedly due to the fact that the products prepared with the above phosphate mixture were by comparative test found to be about 30 F. cooler than products preparedwith ordinary lubricants, such as degras soap. For example, cups stamped from fiat metal sheets, using the ethyl phosphate mixture as the lubricant, were found to have a temperature of from to F. during the working, whereas cups stamped with prior lubricants have working temperatures in the neighborhood of to F.

Another outstanding advantage of the above lubricant compound is that it'may be quickly and easily removed from the metal surface vantageously removed by a simple Washing treat ment. When oil or grease is employed as the lubricant, however, this is not possible, and expensive detergents must be employed with attendant increase in the cost of the cleaning operation. Also there is -considerable possibility that all of the' lubricant will not be removed,

.since the metal surface may appear bright and' clean while still retaining sufllcient residual grease to interfere with proper finishing or coating. Although the above phosphate mixture is readily soluble in water, it has an oily viscosity which gives the desired lubricating effect when it is incorporated in aqueous solutions of suitable concentration.

Although the ethyl phosphate mixture described above decomposes with loss of water to pyrophosphates or metaphosphates upon being heated or annealed, the latter substances are also water soluble and do not present the problems which occur when oil lubricated metal is annealed prior to coating. Thus highly insoluble resins and gummy compounds, which are exalkali metal salt of an alkyl phosphate mixture,

ceedingly difiicult to remove from the metal, are

formed when oil or grease is employed as the lubricant, and such difliculties are avoided in accordance with the present invention. The above mixed ethyl phosphate is also substantially non-corrosive, and difiers noticeably in this respect from any of the inorganic phosphates heretofore employed. Moreover, the ethyl phosphates exert a rust-proofing action on the metal, and render it unnecessary to employ a special rust-proofing agent.

Other alkyl phosphates may of course be employed instead of sodium ethyl phosphate mixtures, the outstanding example of which is sodium methyl phosphate, although propyl and butyl phosphates are also useful in many instances. Thealkali metal salts of weak acids and their hydroxides, as well as the corresponding basically reacting compounds of ammonia may be employed as a neutralizing agent, and if desired, suitable salts for the purposes of this invention may be formed by the use of amines.

The mixed alkali salts of alkyl phosphoric acids may also be employed, the monoethyl so,- dium potassium phosphate giving very good results. Also, mixtures of the phosphatesmay be employed as is outlined above, as well as mixtures of two or more diiferent types, for example, or more of amixture of equal parts of monoand di-ethyl sodium phosphates may be'added to the triethanol amine phosphate salt described above,

and, in general, other mixtures of the phosphates disclosed herein may be prepared to meet special conditions. Although it is in general preferable to neutralize the alkyl prosphate to the pH of about '7, this is not essential.

Since the metal working composition is removed merely by washing, the phosphate may, if desired, be recovered and reused. In general, however, the cost of recovery is not justifled by the valve of the recovered material.

Where the term "alkali metal appears in the claims it will be understood that the ammonium radical is included.

What is claimed is:

1. A bath for coating metal prior to working the same which comprises an aqueous solution containing .at least .about 20% by weight of an alkyl phosphate salt, in which the alkyl group has froml to 5 carbon atoms.

2. A bath for coating metal prior to working the same which comprises an aqueous solution containing at least about 20% by weight of an alkali metal salt of an alkyl phosphate, in which the alkyl group has from 1 to 5 carbon atoms.

- 3. A bath for coating metal prior to working in which the alkyl groups have from 1 to 5 carbon atoms.

4. A bath for coating metal prior to working the same which comprises an aqueous solution containing at least about 20% by weight of triethanolamine ethyl phosphate.

5. A bath for coating metal prior to working the same which comprises an aqueous solution containing at least about 20% by weight of an alkali methyl phosphate.

6. A composition for lubricating metal prior'to working the same which comprises from 20 to 50 parts by weight of an alkali metal salt of an alkyl phosphate, in which the alkyl group has from 1 to 5 carbon atoms, and from 50 to 80 parts by weight of water.

7. A composition for lubricating metal prior to working the same which comprises parts by weight of an alkali metal salt of an alkyl phosphate, in which the alkyl group has from 1 to 5 carbon atoms, .5 part by weight of a wetting agent and 54.5 parts by weight of water.

8. A composition for lubricating metal prior to working the same which comprises 45 parts by weight of sodium ethyl phosphate and .2 part by weight of the sodium salt of an alkylated benzene sulfonate, .25 part by weight of sodium dichromate, and 54.55 parts by weight of water.

9. The method which comprises coating metal with an aqueous solution containing at least about 20% by weight of an alkyl phosphate salt, in which the alkyl group has from 1 to 5 carbon atoms, and cold working the metal while lubricated with said solution.

10. The method which comprises coating metal with an aqueous solution containing at least about 20% by weight of an alkali metal salt of an alkyl phosphate, in which the alkyl group has from 1 to 5 carbon atoms, and cold working the metal while lubricated with said solution.

11. The method which comprises coating metalwith an aqueous solution containing at least about 20% by weight of a sodium ethyl phosphate mixture and coldworking the metal while lubricated with said solution.

12. The method of lubricating metal which to be submitted to a drawing operation which consists in dipping the metal into an aqueous bath containing at least about 20% by weight of an alkali metal salt of an alkyl phosphate, in which the alkyl group has from 1 to 5 carbon atoms, and relatively small amounts of a wetting agent and a rust-proofing agent.

13. A bath for coating metal prior to working the same comprising an aqueous solution containing from 20 to 50% by weight of a sodiumv ethyl phosphate mixture.

14. A bath for coating metal prior to working the same which comprises an aqueous solution containing from 20 to 50% by weight of sodium ethyl phosphate.

15. The method which comprises coating metal with an aqueous solution containing at least about 20% by weight of an alkyl phosphate salt mixture, in which the alkyl groups have from 1 to 5 carbon atoms, and cold working the metal while lubricated with said solution.

CARROLL A. HOCHWALT. 

